The present invention relates to a separation measuring method and a separation measuring apparatus for measuring the separation of objects, which have been displaced relatively, by using optical distance measuring equipments, and more particularly to a separation measuring method and a separation measuring apparatus most suitable for predicting an earthquake by detecting the activity of a fault.
It is said that when the base rock under the ground has been deformed by undergoing an enormous force, for example, of a plate, and a fissure has been formed in the base rock, an earthquake occurs. Therefore, in order to predict an earthquake, it is required to observe strain in the earth crust (that can be determined from the relative movement of the regions on the opposite sides of the active fault and the interval therebetween) at time intervals. Thus, the observation of diastrophism is performed by using, for example, a laser extensometer or an optical distance measuring equipment that can measure distance precisely. In general, a method is used wherein a reference point that serves as a reference of the measurement is set, several observation points that are apart from the reference point are set in regions on the opposite sides of the active fault, these base line net works are observed at time intervals, and accumulated side length changes in the side lengths that are equivalent to the intervals between the reference point and the measurement points are observed.
However, in the above prior observation of diastrophism, distances are measured at time intervals at observation points whose distances from the reference point are known, and changes in the measurements are observed, which is an absolute amount observation. Therefore, to measure the variations of diastrophism, at least two measurements are required, but at each measurement, observation conditions such as temperature, atmospheric pressure, etc. are different inevitably, and therefore there is a problem that the variations of diastrophism cannot be calculated accurately. Thus, the advent of an observation environment has been desired eagerly that allows variations of diastrophism to be simultaneously observed independent of observation condition factors such as temperature, atmospheric pressure, etc.